The Candidate: The candidate is a DVM who has completed clinical training in veterinary pathology and her didactic course work at Washington State University. She is currently about to begin the research phase of a PhD program. This proposal constitutes her plan to complete doctoral research focusing on immunology of infectious disease. Completion will contribute to her long-term goal of independent research and includes a bridge to Research Assistant Professor. Environment: The Department of Veterinary Microbiology and Pathology is known for its contributions to the knowledge of immunology and molecular biology in animal infectious disease. The co-sponsors have experience in performing state-of-the-art research involving equine cytotoxic T lymphocytes (CTLs) and pulmonary immunology of Rhodococcus equi, as well as the training of PhD candidates. Research Proposal: The goal of this research is to define the role of CTLs in the control of R. equi, an intracellular bacterium which infects macrophages and is closely related to Mycobacterium species. R equi causes a pyogranulomatous pneumonia morphologically similar to tuberculosis in both its natural host (the horse), and human AIDS patients. Like Mycobacterium spp., secreted proteins of R equi may escape from the phagosome into the cytosol to be processed and presented as targets for CTL Iysis. Several secreted R equi proteins (i.e. VapC, VapD and VapE) encoded by an 85-kb plasmid have been recently described and may act as targets of cytotoxicity. In addition, the bacterial surface protein, VapA, which is encoded by the same plasmid, was shown to stimulate T lymphocyte proliferation ex viva. The proposed research will test the hypothesis that intrabronchial R equi challenge of immune horses stimulates intrapulmonary CD8+ cytotoxic T lymphocytes specific for secreted proteins encoded by the virulence plasmid. In the specific aims, R equi specific pulmonary CTL will first be characterized for cell surface markers, MHC restriction and the ability to secrete mterferon-garnma. Next we will determine whether or not the virulence plasmid is required for antigen presentation. Finally, vapA, vapC, vap D and vapE expressing retroviral vectors will be used to transduce equine target cells to determine whether R. equi specific CTL Iysis occurs via recognition of these proteins. Results of this research will provide information regarding the control of intracellular bacteria including mycobacteria.